Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

563
FXUS63 KLOT 130457
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1057 PM CST Mon Jan 12 2026

.KEY MESSAGES...

- After unseasonably mild temperatures Tuesday/Tuesday night,
  expect a return to generally much colder temperatures
  Wednesday through the upcoming weekend.

- Chance of wind whipped snow showers/flurries Wed morning,
  greatest coverage eastern IL and northwest Indiana.

- Accumulating lake effect snow expected downwind of Lake
  Michigan late Wednesday through Thursday morning, highest
  chances over northeast Porter County and points eastward.

- Unsettled weather pattern will continue late in the week and
  through the upcoming weekend with periods of gusty winds and
  occasional chances for light snow/flurries.

&&

.DISCUSSION...
Issued at 246 PM CST Mon Jan 12 2026

Upper trough will begin digging into the western/upper Great
Lakes late tonight into Tuesday. Lead shortwave trough is
progged to move across the western Great Lakes late tonight into
Tuesday morning, resulting in an increase in mostly mid-high
level cloudiness. Certainly can`t rule out a few sprinkles,
mainly north of I-88 late tonight into early Wednesday morning,
but given the dry low levels opted to keep grids dry.

Strong sfc low associated with this approaching trough will
deepen to <990mb as it tracks to just north of Lake Superior by
midday Tuesday. Strong pressure gradient associated with this
low will result in strong and gusty southwesterly winds and
associated warm air advection Tuesday. In the wake of the early
morning shortwave, there could be some breaks in the
cloudiness/sunshine by late morning into the afternoon.
GFS/ECMWF/NAM are all running a bit cool with 2m temps, likely a
result of these models initializing a bit of snow cover still.
You can actually see the gradient in temps tomorrow lining up
with where the model thinks there is a Trace to a half inch of
snow on the ground. Given there is no snow cover, felt
comfortable going warmer than most available guidance for high
temps Tuesday (upper 40s-lower 50s). It`s plausible if we get
more sunshine that temps could be a bit warmer. Southwest winds
will ease, but likely remain elevated enough to keep temps
unseasonably mild Tuesday night, likely not falling below
freezing most of the night.

That all will change abruptly very late Tues night over far
northern IL and across the remainder of the CWA Wednesday
morning as a strong cold front rips through the area. While low
level lapse rates will steepen substantially behind the front,
most guidance suggests the convectively unstable layer will
remain rather shallow, capped off a sharp front inversion,
greatly limiting the depth of any cold air stratocumulus and the
resultant snow shower threat. The ECMWF is the lone model with
any measurable QPF and even forecast soundings from the ECMWF
aren`t very impressive with shallow convective cloud depths that
eventually cool sufficiently to contain ice nuclei. NBM pops
have trended downward and barring any shifts in model guidance,
would expect this trend to continue with it looking more like
snow flurries at best Wednesday morning.

Attention will turn to the lake effect potential into the
Indiana snow belt region later Wednesday and especially
Wednesday night into early Thursday morning. Fairly impressive
lake effect parameters with top of the synoptic frontal
inversion up to around 7-8kft with convective cloud layer well
within the DGZ. By Wednesday evening, LES should organize into a
a strong single band with the million dollar question being
where will that band set up. Synoptic flow would tend to favor
LaPorte County, but it looks close for especially northeast
Porter County. Before the more intense single band develops Wed
evening, will likely see lake effect snow showers into northern
Porter County with some accumulations. If models were to trend a
bit more veered with the flow, then that would potentially open
the door to the intense single band and more intense snowfall
rates getting into northeast Porter County for a time Wednesday
evening. The most likely scenario is the heavier snowfall rates
and totals will end up just east of Porter County, so no winter
storm watch issued at this time. Will be something for later
shifts to take another look at.

Long wave trough will become established over eastern North
America through at least early next week. Medium range models
are in good agreement on multiple strong shortwave troughs
digging down the southwestern flanks of the mean long wave
trough in quick succession through the weekend. Models are in
fairly good agreement on a shortwave racing across the upper
Midwest Thursday night into Friday, potentially bringing a quick
hitting shot of WAA driven snow to the area Thur night-Fri
morning. That would be followed by a reinforcing shot of cold
air. Beyond that wave, there is significant spread in the models
and their respective ensembles in timing additional, potentially
potent, shortwaves over the weekend into early next week. The
timing differences result in a low confidence forecast with
respect to exact temps and snow shower chances. Given the low
confidence, no changes were made to NBM. It is worth noting
that there will be some modest moderation in temps in the WAA
regime in advance of these individual waves and more
significantly the potential for blast(s) of bitterly cold air in
their wake. Periodic bouts of snow showers/flurries and strong
winds are likely over the weekend into early next week as well,
but timing of the temperature swings, strong winds, and snow
shower chances will likely need to be fine tuned as we get
closer and model agreement increases.

- Izzi

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1057 PM CST Mon Jan 12 2026

- Gusty WSW winds develop Tuesday turning NW overnight.

- MVFR CIGs develop Tuesday evening and overnight paired with
  the potential for scattered gusty snow showers.

Winds will be generally near and under 10 kt overnight out of
the SW. Sporadic gusts into the 20 kt range will be possible
toward daybreak as low-level flow strengthens overhead. Can`t
rule out a brief period of low-level wind shear if surface winds
are slower to increase than expected early Tuesday morning as
the low-level jet increases to around 45 kt. Have held off on a
formal mention for now. Diurnal mixing should then allow gusts
in the upper 20s to around 30 kt to occur at times through the
daytime hours Tuesday with winds trending more WSW and then W.
The stronger gusts may briefly ease toward sunset but remain
breezy as they turn more WNW Tuesday in the evening.

High clouds will increase in coverage overnight with varying
high cloud coverage (SCT-OVC) expected at times through the
rest of the daytime hours on Tuesday. MVFR CIGs will begin to
drift into northern Illinois Tuesday evening through the
overnight. Can`t rule out spotty light showers late in the
evening with a transition over to gusty snow showers possible
toward early Wednesday morning (30% chance).

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 3 AM to 6 PM CST Tuesday for the IL
     and IN nearshore waters.

     Gale Watch from Wednesday morning through late Wednesday night
     for the IL and IN nearshore waters.

&&

$$

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